Now that we have our sliding barn door in, we need a separate headboard to allow the door to open and close without moving the pillows out of the way.
I roughly followed this DIY tufted headboard guide. Warning: sarcastic rant follows. Isn't it amazing that she made that tufted headboard for only $44? Step one of making a DIY tufted headboard on the cheap -- start with any old headboard you have laying around. Check your privilege, DIY lady. Some of us don't have a cache of free headboards in our basement. New career idea: start dating someone who works at a sawmill, take up woodworking, and make a mint selling furniture on Etsy built from beautiful pilfered live-edge hardwood. OK, rant over.
My actual cost for this was around $200 in materials. I custom built the headboard out of pine 2x2's and 1/4" plywood. The street side had to curve very slightly to match the Airstream wall. I used a compass to transfer the curve on to the headboard and then cut the curve with a jigsaw.
Fabric from the local craft store is 2 yards of charcoal linen, bought on sale. I couldn't find actual egg crate mattress toppers anywhere. The craft store had egg crate foam, but it wasn't cheap. I ended up buying a cheap queen sized foam mattress cover from Walmart for $12, which was just enough to cover the front of the headboard three times, and put batting over the whole thing to smooth it out.
I didn't have as thick of foam or use as much excess fabric as the lady whose guide I was following, so I got a much smoother look. Took some creative folding to avoid raw edges peeking out the sides.